1. Field of the Invention
The invention relates to an organic electroluminescent device. In particular, the invention relates to a phosphorescent organic electroluminescent device.
2. Description of Related Art
An organic electroluminescent device (organic EL device) using an organic material is a promising solid-state emitting type inexpensive and large full-color display device, and has been extensively developed.
In general, when an electric field is applied between electrodes of an organic EL device, electrons are injected from the cathode and holes are injected from the anode. The electrons recombine with the holes in the emitting layer to produce an excited state, and the energy is emitted as light when the excited state returns to the ground state.
An organic EL device includes an emitting layer, a pair of opposing electrodes positioned on either side of the emitting layer, and a layer which transports holes or electrons to the emitting layer. As a specific example of the configuration of the organic EL device, a configuration including anode/hole transporting layer/emitting layer/electron transporting layer/cathode has been known. The hole transporting layer assists in transporting holes generated from the anode to the emitting layer, and the electron transporting layer assists in transporting electrons generated from the cathode to the emitting layer.
Patent document 1 discloses use of a compound having a carbazole group as a host material for the hole transporting layer (electron transporting layer) and the emitting layer. The patent document 1 utilizes a non-conjugated polymer compound for the hole transporting layer to obtain a device with a green emission of 371 m/W. However, the compound of the patent document 1 does not achieve a satisfactory luminous efficiency.
Patent document 2 utilizes a compound having a carbazole group for the hole transporting layer (electron transporting layer). Patent document 3 utilizes a compound having a carbazole group for the hole transporting layer and the emitting layer.
[Patent document 1] JP-A-2004-220931
[Patent document 2] JP-A-2002-203683
[Patent document 3] U.S. Pat. No. 6,863,997
An object of the invention is to provide a low-voltage, high-efficiency, and long-lived organic EL device.